Image display device with light shielding wirings and color filter having resistivity ratio

ABSTRACT

An image display device, particularly an IPS mode LCD, includes a light source, an array substrate including a display region and a peripheral region around the display region, a color filter substrate including a plurality of color filters having different transmissivities, a liquid crystal layer including a plurality of liquid crystal molecules, and an alignment film for aligning the liquid crystal molecules. Characteristically, a light transmittance per unit area in the peripheral region is equivalent to or less than a light transmittance per unit area in the display region.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to an image display device, and moreparticularly, to an IPS (in-plane switching) mode LCD.

2. Description of the Prior Art

An image display device is an optoelectronic device able to transferelectric signals into visible images so that human beings can see theinformation contained in the electronic signals. These days, the typicalimage display device is commonly an LCD, and other display devices, suchas a PDP (plasma display panel) display, an EL (electro luminescence)display, an FED (field emission display), and a DMD (deformable mirrordevice) display.

Among all those image display devices, an active matrix LCD, whichutilizes thin film transistors as switching elements, is popular due toits small size, light weight, and low power consumption. The LCDsubstantially includes two glass substrates, a liquid crystal layerdisposed between the two substrates, and two alignment filmsrespectively disposed on two opposite surfaces of the two substrates fororientating liquid crystal molecules in predetermined directions. Theliquid crystal molecules arranged in predetermined directions arerotated when an electric filed is applied, and thus images are displayedvia light transmittance changes through the liquid crystal layer.

For known art, a TN (twisted nematic) mode LCD has been in use for along time. In the TN mode LCD, the liquid crystal molecules are rotatedin a vertical direction with respect to the substrate. However, thisleads to problems of narrow viewing angles and color distortions.

In order to solve these problems, Japanese patent (publication No.07-36058) has proposed an IPS mode LCD. In the Japanese patent, the IPSmode LCD includes a plurality of pixel electrodes and a plurality ofcommon electrodes arranged in parallel to the pixel electrodes in anarray substrate. A voltage is applied between the pixel electrode andthe common electrode so that a parallel electric field, which rotatesthe liquid crystal molecules, is generated above the array substrate.Since the liquid crystal molecules are rotated in a plane approximatelyparallel to the array substrate, the problems of color distortions andnarrow viewing angles are reduced. Therefore, the IPS mode LCD issuitable for use in large-sized displays.

For the IPS mode LCD, however, an uneven brightness defect occurs when alarge-sized screen with fine image qualities is desired. Presumably, theuneven brightness defect results from the existence of impurity ions.FIG. 14 is a schematic diagram illustrating an image display conditionof a conventional LCD. As shown in FIG. 14, when a white image isdisplayed in a display region 102, red color unevenness defects 104appears around the display region 102. These red color unevennessdefects 104 degrade the image quality of the IPS mode LCD.

SUMMARY OF INVENTION

It is therefore a primary object of the claimed invention to provide animage display device to prevent the aforementioned uneven brightnessproblem.

According to claim 1, an image display device is provided. The imagedisplay device includes a light source, an array substrate including adisplay region and a peripheral region around the display region, acolor filter substrate including a plurality of color filters havingdifferent transmissivities, a liquid crystal layer including a pluralityof liquid crystal molecules, and an alignment film for aligning theliquid crystal molecules. Characteristically, a light transmittance perunit area in the peripheral region is equivalent to or less than a lighttransmittance per unit area in the display region.

By virtue of the image display device recited in claim 1, the lighttransmittance per unit area in the peripheral region is equivalent to orless than a light transmittance per unit area in the display region, soas to inhibit impurity ions from traveling from the peripheral region tothe display region. Consequently, the uneven brightness problem isreduced.

According to claim 2, the array substrate recited in claim 1 includes afirst light-shielding wiring layout arranged in the display region, anda second light-shielding wiring layout arranged in the peripheralregion. Characteristically, an occupied area per unit area of the secondlight-shielding wiring layout in the peripheral region is equivalent toor greater than an occupied area per unit area of the firstlight-shielding wiring layout in the display region.

According to claim 3, the image display device recited in claim 2,wherein the first light-shielding wiring layout and the secondlight-shielding wiring layout comprise at least one of an activeelement, a passive element, and a wiring.

According to claim 4, an image display device is disclosed. The imagedisplay device includes a light source, an array substrate including adisplay region and a peripheral region around the display region, acolor filter substrate including a plurality of color filters havingdifferent transmissivities, a liquid crystal layer including a pluralityof liquid crystal molecules, and an alignment film for aligning theliquid crystal molecules. Characteristically, a resistivity ratio of thecolor filter having a highest resistivity to the color filter having alowest resistivity is set according to a difference between a lighttransmittance per unit area in the peripheral region and a lighttransmittance per unit area in the display region.

By virtue of the image display device recited in claim 4, theresistivity ratio of the color filter having the highest resistivity tothe color filter having the lowest resistivity is set according to thedifference between the light transmittance per unit area in theperipheral region and the light transmittance per unit area in thedisplay region, so as to inhibit impurity ions from traveling from theperipheral region to the display region. Consequently, the unevenbrightness problem is reduced.

According to claim 5, the relation between the resistivity ratio of thecolor filter having the highest resistivity to the color filter havingthe lowest resistivity and the difference between the lighttransmittance per unit area in the peripheral region and the lighttransmittance per unit area in the display region is expressed byρ_(max)/ρ_(min)<10^((4100/(If−Ip)+0.05))

-   -   wherein        -   ρ_(max) is the highest resistivity having units of Ω·cm;        -   ρ_(min) is the lowest resistivity having units of Ω·cm;        -   I_(f) is the light transmittance in the peripheral region            having units of cd/mm; and        -   I_(p) is the light transmittance in the display region            having units of cd/mm.

According to claim 6, an image display device is provided. The imagedisplay device includes a light source, an array substrate including adisplay region and a peripheral region around the display region, acolor filter substrate including a plurality of color filters havingdifferent transmissivities, a liquid crystal layer including a pluralityof liquid crystal molecules, and an alignment film for aligning theliquid crystal molecules. Characteristically, the alignment film is onlypositioned in the display region.

By virtue of the image display device recited in claim 6, the alignmentfilm is only positioned in the display region, so that the unevenbrightness problem due to the contamination of impurity ions coming fromthe peripheral region is prevented.

According to claim 7, the image display device is an IPS mode LCD.

The image display device reduces electric filed deviations due toimpurity ions by means of controlling the extension of impurity ions. Asa result, the image display device is able to exhibit high qualityimages without suffering the red color unevenness phenomenon.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a top view of an array substrate of an LCD according toEmbodiment 1.

FIG. 2 is a schematic diagram of a wiring layout in an area A shown inFIG. 1.

FIG. 3 is a cross-sectional view of the LCD of Embodiment 1.

FIG. 4 is a schematic diagram illustrating variations of electric fieldmagnitude of the conventional LCD.

FIG. 5 is a schematic diagram illustrating whether the red colorunevenness defect happens to LCDs having different ratios of occupiedarea S_(f) to occupied area S_(p) while displaying a white image.

FIG. 6 is a cross-sectional view of an LCD according to Embodiment 2.

FIG. 7 is a schematic diagram illustrating whether the red colorunevenness defect happens to LCDs having different light transmittancedifferences (I_(f)−I_(p)) and different resistivity ratios whiledisplaying a white image.

FIG. 8 is a schematic diagram illustrating areas being heated andshielded in the display region.

FIG. 9 is a schematic diagram illustrating a relation between the volumeresistivity and time in the R pixels, G pixels, and B pixels of aconventional LCD at a humidity of 85%.

FIG. 10 is a schematic diagram illustrating variations of electric fieldmagnitude of the conventional LCD.

FIG. 11 is a cross-sectional view of an LCD according to Embodiment 3.

FIG. 12 is a schematic diagram illustrating an array substrate of aconventional LCD with an alignment printed region.

FIG. 13 is a schematic diagram illustrating the array substrate shown inFIG. 12.

FIG. 14 is a schematic diagram illustrating an image display conditionof a conventional LCD.

DETAILED DESCRIPTION

Please refer to the drawings of the present invention. In theembodiments, an IPS mode LCD is merely an example, but not a limitationto the present invention. In the drawings, like elements are denoted bylike numerals. In addition, the drawings are schematic diagrams, andtherefore the dimensions and ratios of components may not be identicalto real ones.

[Embodiment 1]

In Embodiment 1, an occupied area per unit area of wirings in theperipheral region is either approximately equivalent to or greater thanan occupied area per unit area of wirings in the display region foradjusting the light transmittance passing through the display region andthe peripheral region. This inhibits the movement of impurity ions thatis presumed to cause the uneven brightness defect.

FIG. 1 is a top view of an array substrate of an LCD according toEmbodiment 1. As shown in FIG. 1, an array substrate 1 includes adisplay region 2 composed of a plurality of pixels (not shown) and aperipheral region 3 having a plurality of input terminals (not shown)for receiving external electric signals. The array substrate 1 furtherincludes a sealant coating region 4 in which a sealant is coatedthereon. The peripheral region 3 is positioned between the displayregion 2 and the sealant coating region 4.

FIG. 2 is a schematic diagram of wirings disposed in an area A shown inFIG. 1. As shown in FIG. 2, gate lines 5 and signal lines 6 are arrangedin a matrix, and each pixel includes a TFT 8. Since the LCD is an ISPmode LCD, the LCD includes a plurality of pixel electrodes (not shown)and a plurality of common electrodes 7 positioned in line with the pixelelectrodes. In addition, the gate lines 5 are extended to connect inputterminals (not shown) in the peripheral region 3. Besides, there is aplurality of dummy patterns 9 in the peripheral region 3. The dummypatterns 9 are used to adjust the occupied area of the wirings so thatthe occupied area of the wirings per unit area in the peripheral region3 (hereinafter referred to as S_(f)) is approximately equivalent to orgreater than the occupied area of the wirings per unit area in thedisplay region 2 (hereinafter referred to as S_(p)). The wirings includenot only the gate lines 5, the signal lines 6, the common electrodes 7,and the pixel electrodes, but also the TFTs 8, passive elements (e.g.capacitors), and the dummy patterns 9. The function of the dummypatterns 9 is to adjust the occupied areas S_(f) and S_(p), thus thedummy patterns 9 are light shielding, and the line width of the dummypatterns 9 is not necessarily identical to other wirings disposed in theperipheral region 3.

FIG. 3 is a cross-sectional view of the LCD of Embodiment 1. As shown inFIG. 3, an array substrate 1 and a CF (color filter) substrate 11 arebonded together with a sealant 12. A liquid crystal layer 16 includingliquid crystal molecules is filled between the array substrate 1 and theCF substrate 11. The CF substrate 11 includes a BM (black matrix) layer13, a color filter layer 14 including a plurality of color filtershaving different transmissivities, and a passivation layer 15. The LCDfurther includes two alignment films 17 respectively positioned on thesurface of the array substrate 1 and the surface of the CF substrate 11in contact with the liquid crystal molecules, so as to orientate theliquid crystal molecules. The array substrate 1 includes a plurality ofcommon electrodes 7, signal lines 6, and pixel electrodes 10 in thedisplay region 2. By applying a voltage to the common electrode 7 andthe pixel electrode 10, an electric field parallel to the arraysubstrate 1 is generated between the common electrodes 7 and the pixelelectrodes 10. Consequently, the liquid crystal molecules of the liquidcrystal layer 16 rotate. In addition, the array substrate 1 furtherincludes gate lines 5 and dummy patterns 9 in the peripheral region 3.

Generally, the light coming from a light source of a backlight unit (notshown) evenly enters the liquid crystal layer 16 through the arraysubstrate 1. With the dummy patterns 9, that make the occupied areaS_(f) approximately equivalent to or larger than the occupied areaS_(p), disposed in the peripheral region 3, a light transmittance perunit area in the peripheral region 3 (hereinafter referred to as I_(f))is equivalent to or less than a light transmittance per unit area in thedisplay region 2 (hereinafter referred to as I_(p)). By making I_(f)equal to or smaller than I_(p), the uneven brightness defect due to themovement of impurity ions towards the display region 2 is inhibited. Thereason for the reduction of the uneven brightness defect is detailed inthe following.

The red color unevenness defect is inferred to be from impurity ionswhile the LCD is operating. Specifically, the emission of the impurityions from the peripheral region to the liquid crystal layer is driven bybacklight unit illumination. The higher the light transmittance is, themore impurity ions enter the liquid crystal layer. The accumulation ofthe impurity ions in the display region leads to the red colorunevenness defect.

Therefore, upon close inspection of the cause of the red colorunevenness defect, an experimental result is obtained. Please refer toTable 1. Table 1 shows an experimental result of a conventional LCD insequence from 1 to 3 after applying a voltage to each wiring or/andlighting up the light source to examine if the red color unevennessdefect appears in the display region when displaying a white image. Itis important to note that the conventional LCD does not include dummypatterns in the peripheral region, and therefore the occupied area S_(f)is smaller than the occupied area S_(p). In addition, all results arefrom experiments at 50 degrees Celsius for 100 hours. In Experiment 1,each wiring is applied with a voltage, and the light source is off.Subsequently, the voltage applied to the wirings is ceased, and thelight source is on for Experiment 2. Following that, a voltage isapplied to each wiring again, and the backlight is off for Experiment 3.

TABLE 1 Experiment Voltage Light source Red color unevenness defect 1 OnOff No 2 Off On No 3 On Off Yes

As shown in Table 1, the red color unevenness defect while displaying awhite image does not appear in Experiment 1. In Experiment 1, a voltageis applied to the wirings for generating an electric filed, and thelight source is off. Presumably the electric filed is not the cause ofthe red color unevenness defect. The red color unevenness defect whiledisplaying a white image also does not appear in Experiment 2. InExperiment 2, the light source, which is inferred to cause the emissionof impurity ions, is on, however, the red color unevenness does notappear. The explanation for this experimental result is that the amountof impurity ions may not cause the red color unevenness defect in thedisplay region.

On the other hand, the red color unevenness defect does appear whiledisplaying a white image in Experiment 3. Thus, the presence of the redcolor unevenness defect is inferred to be caused by the movement ofimpurity ions induced in Experiment 2 into the display region under theeffect of the electric filed. In the conventional LCD, the occupied areaS_(f) is less than the occupied area S_(p), meaning the lighttransmittance I_(f) is greater than the light transmittance I_(p).Therefore, In Experiment 2, the majority of the impurity ions due to thebacklight exist in the peripheral region. In Experiment 3, the electricfiled drives the impurity ions to move into the display region. FIG. 4is a schematic diagram illustrating variations of electric fieldmagnitude of the conventional LCD. As shown in FIG. 4, impurity ionsemitted from a peripheral region 3 a slowly move to a display region 2a, and accumulate on the surface of the CF substrate 11 facing the arraysubstrate 1. These accumulated impurity ions result in electricdeflections, and disturb the electric filed while displaying an image.For instance, if the electric filed has a desired magnitude of A₁ asshown in FIG. 4, the accumulated impurity ions disturb the electricfield, making the electric field have an actual magnitude of A₂. Thedisorder of the electric field further deranges the alignment of theliquid crystal molecules of the liquid crystal layer 16. Consequently,the brightness is partially reduced, and the red color unevenness defecttherefore appears when displaying a white image.

In Embodiment 1, the occupied area S_(f) is either equivalent to orgreater than the occupied area S_(p). In the case that the occupied areaS_(f) is equivalent to the occupied area S_(p), the light transmittanceI_(f) is approximately equivalent to the light transmittance I_(p)Namely, the emitted impurity ions are about equal in the display region2 and in the peripheral region 3. Therefore, the distributions ofimpurity ions in the display region 2 and the peripheral region 3 areapproximately equal. In other words, few impurity ions travel from theperipheral region 3 towards the display region 2, and thus electricdeflections do not occur. In addition, in the case that the occupiedarea S_(f) is greater than the occupied area S_(p), the lighttransmittance I_(f) is less than the light transmittance I_(p). Thismeans the emitted impurity ions in the peripheral region 3 are evenfewer than in the display region 2. In that case, the impurity ions inthe peripheral region 3 do not move towards the display region 2 evenwhen a voltage is applied to each wiring. Consequently, the electricdeflections do not show up.

In Embodiment 1, the variations of the electric field never happens eventhough a voltage is applied to the common electrodes 7 and the pixelelectrodes 10 and the light source is turned on. As a result,high-quality display images without the occurrence of the red colorunevenness defect is realized when displaying a white image.

FIG. 5 is a schematic diagram illustrating whether the red colorunevenness defect happens to LCDs having different ratios of occupiedarea S_(f) to occupied area S_(p) while displaying a white image. InFIG. 5, the longitudinal axis represents a product of lighttransmittance and pixel numbers per inch. The higher the product is, thehigher the difference between the occupied area S_(p) and the occupiedarea S_(f) is. Samples a to g are ranked by the ratio of the occupiedarea S_(f) to the occupied area S_(p), in which samples a and b have anoccupied area S_(f) less than an occupied area S_(p), and samples c, d,e, f, and g have an occupied area S_(f) equivalent to or greater than anoccupied area S_(p).

As shown in FIG. 5, the red color unevenness defect occurs whendisplaying a white image in samples a and b having occupied area S_(f)less than occupied area S_(p). On the other hand, the red colorunevenness defect does not occur when displaying a white image insamples c, d, e, f, and g having occupied area S_(f) equivalent to orgreater than occupied area S_(p). This result is consistent with theassumption recited earlier. For cases in which the occupied area S_(f)is equivalent to or greater than the occupied area S_(p), thedistributions of impurity ions in the display region 2 and theperipheral region 3 are approximately equal, and few impurity ionstravel from the peripheral region 3 towards the display region 2. Thus,the electric deflections, which incur the red color unevenness defect,do not occur.

Accordingly, Embodiment 1 modifies the light transmittance If to beapproximately equal to or less than the light transmittance I_(p) byvirtue of adjusting the occupied area S_(f) approximately to be equal toor greater than the occupied area S_(p). Consequently, the amount of theimpurity ions traveling from the peripheral region 3 to the displayregion 2 due to light irradiation is inhibited. In this case, the redcolor unevenness defect when displaying a white image, and the unevenbrightness problem are both reduced. This enables the LCD according toEmbodiment 1 to display high-quality images.

According to Embodiment 1, the dummy patterns 9 are positioned in theperipheral region 3 so that the occupied area S_(f) is equal to orgreater than the occupied area S_(p). However, the present invention isnot limited to Embodiment 1, and the occupied area S_(f) can also bemodified by enlarging the line width of the gate lines 5 or the signallines 6 in the peripheral region 3. In this case, the lighttransmittance I_(f) is also equivalent to or less than the lighttransmittance I_(p), so as to inhibit impurity ions from moving from theperipheral region 3 to the display region 2. Accordingly, the red colorunevenness defect when displaying a white image is reduced.

[Embodiment 2]

In Embodiment 1, the movement of the impurity ions from the peripheralregion towards the display region is prohibited by virtue of adjustingthe occupied area S_(f) in the peripheral region and the occupied areaS_(p) in the display region. In Embodiment 2, on the other hand, aresistivity ratio of the color filter layer is modified to prevent theimpurity ions in the display region from partially deviating, so thatthe red color unevenness defect is reduced.

FIG. 6 is a cross-sectional view of an LCD according to Embodiment 2. Asshown in FIG. 6, dummy patterns are not provided in the peripheralregion 3. Therefore, the light transmittance I_(f) in the peripheralregion 3 is greater than the light transmittance I_(p) in the displayregion 2. In addition, the color filter layer includes a plurality of R(red) color filters 24 r having a resistivity r, G (green) color filters24 g having a resistivity g, and B (blue) color filters 24 b having aresistivity b. In Embodiment 2, a resistivity ratio of the lowestresistivity color filter to the highest resistivity color filter(hereinafter referred to as resistivity ratio) is set in view of thedifference of the light transmittance I_(p) and the light transmittanceI_(f) as shown in the following equation (1):ρ_(max)/ρ_(min<)10^((4100/(If−Ip)+0.05))  (1)

-   -   wherein        -   ρ_(max) is the highest resistivity having units of Ω·cm; and        -   ρ_(min) is the lowest resistivity having units of Ω·cm.

FIG. 7 is a schematic diagram illustrating whether the red colorunevenness defect happens to LCDs having different light transmittancedifferences (I_(f)−I_(p)) and different resistivity ratios whiledisplaying a white image. In FIG. 7, sample groups h to 1 represent LCDshaving different light transmittance differences (I_(f)−I_(p)) anddifferent resistivity ratios. As shown in FIG. 7, with regard to samplegroup h, the difference between I_(f) and I_(p) is negative, and the redcolor unevenness defect does not occur when displaying a white image.This supports the conclusion of Embodiment 1 that the movement ofimpurity ions from the peripheral region to the display region isinhibited when the light transmittance I_(f) is less than the lighttransmittance I_(p).

As for sample groups i, j, k, and l, each of these has a positive lighttransmittance difference. In addition, curve 1 a is a boundary: the redcolor unevenness defect occurs over curve 1 a, and it does not occurunder curve 1 a. In conclusion, to inhibit the red color unevennessdefect, the relation between the light transmittance difference and theresistivity ratio has to fulfill equation (1).

In practice, sometimes the resistivity ratio of the color filter layeris higher if different materials are adopted. For a higher resistivityratio, the light transmittance difference must be set in accordance withequation (1), so as to inhibit the red color unevenness defect.Therefore, Table 2 illustrates the occupied area difference(S_(f)−S_(p)) and the light transmittance difference (I_(f)−I_(p)) ofsample groups h, i, j, k, and l.

TABLE 2 Light transmittance Occupied area difference difference [cd/m²]Sample group h −0.17 −930 −0.13 −730 Sample group i 0.09 730 0.12 8000.14 950 Sample group j 0.32 2300 Sample group k 0.39 3500 Sample groupl 0.46 3800

Accordingly, the occupied area difference and the light transmittancedifference are roughly proportional. Therefore, for a known resistivityratio, the occupied area difference, which represents the lighttransmittance difference, can be modified to meet equation (1), so as toreduce the red color unevenness defect. In addition, even though thelight transmittance difference is inevitably higher due to circuitdesign requirements, the red color unevenness defect when displaying awhite image still can be reduced by selecting different materials forthe color filter layer.

The relation between the resistivity ratio, the light transmittancedifference, and the occurrence of the red color unevenness defect isdetailed in the following. For ensuring variations of brightness in eachpixel, which is assumed to be the cause of the red color unevennessdefect, the display region of a conventional LCD is first heated andshielded in predetermined areas. FIG. 8 is a schematic diagramillustrating areas heated and shielded from light in the display region2. In FIG. 8, an area A is heated to a temperature ranging from 55 to 75degrees Celsius, and the area outside the area A is maintained at atemperature ranging from 25 to 35 degrees Celsius. In addition, an areaB is a light-shielded area. Therefore, an area C where the area A andthe area B overlap is heated and light-shielded. Subsequently, thebrightness in the area A and the area C of R pixels, G pixels, and Bpixels are measured. In the G pixels, a brightness reduction isobserved. Table 3 shows the brightness Y_(G) of the area A and the areaC in the G pixels.

TABLE 3 Area Light-shielded Heated Brightness Y_(G) [cd/m²] A No Yes 133C Yes Yes 150

As shown in Table 3, compared to the area C that is heated andlight-shielded, a brightness Y_(G) reduction in the area A is observed.This result shows that the impurity ions caused by the backlightparticularly accumulate in the G pixels, rather than in the R pixels andthe B pixels. As a result, the brightness Y_(G) in the G pixels isreduced, causing the red color unevenness defect while displaying awhite image.

Therefore, to determine the differences between the R pixels, B pixels,and G pixels, volume resistivities of the R pixels, G pixels, and Bpixels can be measured to reveal a significant difference. FIG. 9 is aschematic diagram illustrating a relation between the volume resistivityand time in the R pixels, G pixels, and B pixels of a conventional LCDat a humidity of 85%. Volume resistivity is the resistivity divided bythe thickness of the color filter layer in cm. Curves I_(R) and I_(R)′illustrate the variations of an R color filter with time. Curves I_(G)and I_(G)′ illustrate the variations of a G color filter with time.Curves I_(B) and I_(B)′ illustrate the variations of a B color filterwith time. Curves I_(R), I_(G), and I_(B) are measured at 70 degreesCelsius, and curves I_(R)′, I_(G)′, and I_(B)′ are measured at 50degrees Celsius. As illustrated by curves I_(G) and I_(G)′, the G colorfilter is irrelevant to the atmosphere. In addition, compared to the Rcolor filter and the B color filter, the volume resistivity of the Gcolor filter is one tenth that of the R color filter or the B colorfilter. Since the thickness of each color filter is about equal, and sois the area of each pixel, the resistivity of the G color filter,compared to that of the R color filter and the B color filter, isdramatically reduced.

As shown in FIG. 9, due to the accumulation of impurity ions, theresistivity of the G color filter, compared to that of the R colorfilter and the B color filter, is reduced greatly. Therefore, it isassumed that the accumulated impurity ions are relevant to theresistivity of the pixel having the accumulated impurity ions therein.Specifically, the impurity ions tend to accumulate in pixels with lowresistivity. FIG. 10 is a schematic diagram illustrating variations ofelectric field magnitude of the conventional LCD. As shown in FIG. 10,in the conventional LCD, the light transmittance I_(f) is greater thanthe light transmittance I_(p), and impurity ions generated in theperipheral region tend to move to the display region of the G colorfilter, which has a low resistivity 204 g, instead of the R color filterhaving a higher resistivity 204 r or the B color filter having a higherresistivity 204 b. In that case, when a voltage is applied to eachwiring for generating an electric field, the electric field in a B pixelhas a magnitude A₃, while the electric field in a G pixel has an actualmagnitude A₄ under the influence of the impurity ions. Impurity ionslead to disorder in the liquid crystal molecules, thereby causingbrightness reduction and the red color unevenness defect. Based on theabove assumption, the accumulation of impurity ions can be reduced bydiminishing the resistivity ratio of the color filters.

In Embodiment 2, the light transmittance difference and the resistivityratio have the relation as expressed in equation (1). Therefore, toprevent the accumulation of impurity ions in the display region 2,reducing the resistivity ratio is a useful approach. Accordingly, thelocal brightness reduction problem is improved, and so is the red colorunevenness defect. In addition, if the resistivity ratio is inevitablyhigh due to the material characteristics of the color filters, adjustingthe occupied area difference of the wirings to meet equation (1) isanother approach to reduce the red color unevenness defect. Inconclusion, high-quality images without the red color unevenness defectcan be obtained by adjusting the resistivity ratio and the occupied areadifference according to Embodiment 2.

Furthermore, the relation between the resistivity ratio and the lighttransmittance difference is defined by equation (1) in Embodiment 2, butthe present invention is not limited by equation (1) if differentmaterials are adopted for making the LCD. The essence of the presentinvention is to reduce the red color unevenness defect while displayinga white image either by adjusting the resistivity ratio according to thelight transmittance difference, or adjusting the light transmittancedifference according to the resistivity ratio.

[Embodiment 3]

In both Embodiment 1 and Embodiment 2, the red color unevenness defectis reduced by inhibiting the move and the accumulation of the impurityions. In Embodiment 3, on the other hand, the red color unevennessdefect is reduced by reducing emissions of the impurity ions.

FIG. 11 is a cross-sectional view of an LCD according to Embodiment 3.As shown in FIG. 11, alignment films 37 a and 37 b are only formed in adisplay region 2, rather than in a peripheral region 3. FIG. 12 is aschematic diagram illustrating an array substrate 1 of a conventionalLCD with an alignment printed region 38 a. As shown in FIG. 12, analignment film (not shown) is printed within the alignment film printedregion 38 a, which covers the display region 2 and the peripheral region3, on an array substrate 1. Red color unevenness defects 39 a to 39 doccur around the display region 2. FIG. 13 is a schematic diagramillustrating the array substrate 1 shown in FIG. 12. As shown in FIG.13, the alignment film printed region 38 a is shifted leftward, forminga new alignment film printed region 38 b. In addition, a CF substrate(not shown) also includes a corresponding alignment film printed region(not shown). It can seen in FIG. 13 that the red color unevennessdefects 39 b, 39 c, and 39 d occur in the upper, lower, and left sides,but not in the right side of the display region 2. Therefore, thealignment film is construed as a cause of the emission of impurity ions.

The alignment films 37 a and 37 b, which are assumed to be the cause ofthe emission of impurity ions, are only formed in the display region 2in Embodiment 3, so as to inhibit the emission of impurity ions. This isdifferent from Embodiment 1 and Embodiment 2 in which the impurity ionsare inhibited from moving from the peripheral region 3 towards thedisplay region 2. Therefore, the LCD has a reduction in the unevenbrightness problem and the red color unevenness defect.

In summary, the LCDs of Embodiment 1, Embodiment 2, and Embodiment 3 ofthe present invention inhibit the movement, accumulation, or generationof impurity ions, and thus reduce the red color unevenness defect due tothe brightness reduction in green pixels being prevented. Furthermore,the brightness reduction in red pixels and blue pixels can also beavoided. Consequently, high-quality images without uneven brightness canbe achieved.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. An image display device comprising: a lightsource; an array substrate comprising a display region and a peripheralregion around the display region, wherein the array substrate comprises:a first light-shielding wiring layout arranged in the display region ofthe array substrate; and a second light-shielding wiring layout arrangedin the peripheral region of the array substrate, an occupied area perunit area of the second light-shielding wiring layout in the peripheralregion being equal to or greater than an occupied area per unit area ofthe first light-shielding wiring layout in the display region, whereinthe second light-shielding wiring layout includes dummy patterns formedon the array substrate in the peripheral region, the dummy patterns toadjust the occupied area per unit area of the second light-shieldingwiring layout to be equal to or greater than the occupied area per unitarea of the first light-shielding wiring layout; a color filtersubstrate comprising a plurality of color filters having differenttransmissivities; a liquid crystal layer comprising a plurality ofliquid crystal molecules; and an alignment film for orientating theliquid crystal molecules; wherein a light transmittance per unit area inthe peripheral region of the array substrate is equal to or less than alight transmittance per unit area in the display region of the arraysubstrate.
 2. The image display device of claim 1, wherein the firstlight-shielding wiring layout and the second light-shielding wiringlayout comprise at least one of an active element, a passive element,and a wiring.
 3. The image display device of claim 1, wherein the imagedisplay device is an IPS (in-plane switching) mode LCD (liquid crystaldisplay).
 4. The image display device of claim 1, wherein the liquidcrystal layer is disposed between the array substrate and the colorfiller substrate, and wherein light passing from the light sourcethrough the array substrate to the liquid crystal layer is subject tothe light transmittance per unit area in the peripheral region and thelight transmittance per unit area in the display region.
 5. The imagedisplay device of claim 4, wherein the color filter substrate has ablack matrix (BM) layer that is spaced apart from the array substrate byat least the liquid crystal layer.
 6. An image display devicecomprising: a light source; an array substrate comprising a displayregion and a peripheral region around the display region; a color filtersubstrate comprising a plurality of color filters having differentresistivities; a liquid crystal layer comprising a plurality of liquidcrystal molecules; and an alignment film for orientating the liquidcrystal molecules; wherein a resistivity ratio of the color filterhaving a highest resistivity to the color filter having a lowestresistivity is set according to a difference between a lighttransmittance per unit area in the peripheral region and a lighttransmittance per unit area in the display region.
 7. The image displaydevice of claim 6, wherein the image display device is an IPS (in-planeswitching) mode LCD (liquid crystal display).
 8. An image display devicecomprising: a light source; an array substrate comprising a displayregion and a peripheral region around the display region; a color filtersubstrate comprising a plurality of color filters having differentresistivities; a liquid crystal layer comprising a plurality of liquidcrystal molecules; and an alignment film for orientating the liquidcrystal molecules; wherein a resistivity ratio of the color filterhaving a highest resistivity to the color filter having a lowestresistivity is set according to a difference between a lighttransmittance per unit area in the peripheral region and a lighttransmittance per unit area in the display region, wherein the relationbetween the resistivity ratio of the color filter having the highestresistivity to the color filter having the lowest resistivity and thedifference between the light transmittance per unit area in theperipheral region and the light transmittance per unit area in thedisplay region is expressed by:ρ_(max)/ρ_(min)<10^((4100/(If−Ip)+0.05)) wherein ρ_(max) is the highestresistivity; ρ_(min) is the lowest resistivity; I_(f) is the lighttransmittance in the peripheral region; and I_(p) is the lighttransmittance in the display region.